Device for Automatic Calibration of Scopes for Firearms

ABSTRACT

This patent defines a device for automatic calibration of optical sights for firearms. Only one shot has to be fired to achieve this. The device can be integrated with an optical sight or fitted as a separate unit mounted on the sight. 
     The device consists of a digital camera (e.g. CCD), a beam splitter, a microprocessor including a memory for camera images and computer software, servo motors including a gear mechanism, an electrical switch and light emitting diodes and a shot detecting sensor. In the digital sight application, the device also includes a display unit while servo motors, gear mechanism, light emitting diodes and beam splitter are excluded. 
     The calibration procedure involves firing a round at a target consisting of a rectangular white surface on a dark background at the chosen range. The camera saves the last image immediately before the firing moment and compares the cross-hairs position with that of a following image from which the projectile point of impact can be found. After calculations that determines the error between point of aim and the projectile point of impact—which are based on image analysis only—the position of the cross-hairs is adjusted by servomotors to align with the detected projectile impact point position. In the digital sight application, the cross-hairs is simply re-drawn at the new correct location on the display. The weapon and the optical sight are now calibrated at the chosen range.

TECHNICAL DOMAIN

The device offers a means for automatic calibration of an optical sight for firearms, by firing one round only.

TECHNICAL STANDPOINT

To zero-in, or calibrate, a firearm equipped with an optical sight, typically a riflescope, is usually a tedious and to some extent error prone procedure. Several rounds are usually needed for a successful calibration. Hunters then usually fire a couple of high priced soft point rounds to confirm the calibration.

The device described in this application offers shooters the possibility of getting the optical sight (riflescope) automatically calibrated, by firing one round only, at a defined target.

DESCRIPTION OF THE INVENTION

To achieve an automatic calibration of an optical sight for firearms, a traditional optical sight needs the following additional items, se FIG. 1. A beam-splitter (1) lets the shooter and the image processing system view the same scene. The image is fed into a camera (2) (e.g. a CCD camera) for image capture. A processing unit with sufficient memory and software (3) analyzes the image and determines the error (i.e. calculates the need for calibration). Servo motors (4) with gears (5) can be used to operate the adjustment screws and the traditional mechanical reticle element (9). A switch is used to initiate the automatic calibration sequence (6). Lamps (8) (e.g. diodes) indicate the calibration result. The device is powered by a built-in or external electrical power source (7).

By reticle is meant all existing variants of optical reticles.

The calibration sequence is described by the following instruction to the shooter:

-   -   Arrange a target (typically: a white square surface against a         dark background) and assume firing position at the range for         which the firearm is to be calibrated.     -   Initiate the calibrating function by pressing the switch.     -   Aim & fire a round at the target.     -   After firing the round, aim again at the target and identify the         bullet hole visually.     -   Hold the reticle steady at the target, when the green lamp         lights up—the calibration is successful. If the red lamp lights         up, repeat the sequence.     -   The calibrating function is shut off by pressing the switch         again.

Function: When the calibration procedure is initiated by the switch, the processing unit and camera start up. The camera immediately starts taking images (with a typical interval between images of 40 ms) and stores them in a FIFO queue (First In, First Out).

The processing unit detects that a round has been fired when the target suddenly disappears from the view (it happens very fast; i.e. from one image to the other). Alternatively an embedded sensor can be used to register this event.

The last exposure before the shot is stored for later analysis; the edges of the white target area are identified by contrast with the darker background.

After firing the round, the shooter resumes the aiming position while the camera continues to take images and to store them in the FIFO queue. The best image after firing is identified and is then compared with the best image before firing. The bullet-hole position on the target is identified by variation in contrast (black dot on the white surface).

While the shooter holds the reticle on the target, the processing unit calculates the needed adjustment. This means both horizontal and vertical adjustments in “clicks”, to align the bullet hole with the reticle. Since the reticle position is determined relative to the target in the entire field of view—both before and after firing the round—the needed adjustment can be calculated independent of range and riflescope magnification. (However, the target must not be moved and that the shooter must not change position during the calibration procedure).

Since this innovation relies on image analysis only, by detection of the actual projectile point of impact—i.e. the bullet hole in the target—all physical effects affecting the projectile trajectory is inherently taken into account, without explicit knowledge of their magnitude (scope magnification, distance, ballistics, temperature, wind direction, wind intensity, barrel or bullet irregularities, etc). We close the feedback loop by using the image of the actual projectile point of impact, thus including the effect of all previously mentioned parameters on the bullet trajectory.

Also, the firing moment can be detected trough image analysis only. Using image processing techniques of a known type, the sudden changes in target position between two consecutive images, clearly indicates the rapid movement of the field of view, due to the recoil. Thus, the last image before the firing moment can be acquired, and consequently the point of aim before firing is captured in that image.

The servo motors are then activated so that the adjustment screws are turned the needed number of “clicks” in both horizontal and vertical directions. A green lamp lights up as an indication of a successful calibration. If the identification of the bullet-hole fails, a red lamp lights up, and the procedure needs to be repeated (a possible cause for failure might be that the bullet has missed the target).

When the shooter finally presses the switch again, the calibration system is shut down (power off).

Alternative Arrangements:

-   -   1. The same calibration function can be achieved in an         embodiment comprising of a fully digital optical sight with         traditional fixed or zoom lens for riflescopes, and a display in         the viewfinder with a digital reticle.         -   This can be implemented by a camera (2) placed directly in             the line of sight, a processing unit with memory and             software (3), and a display (10) (typically a LCD—Liquid             Crystal Display) in the viewfinder instead of a conventional             lens. In this case the need for indicator lamps is             eliminated since the calibration result can be displayed             directly on the display. The switch (6) and power source (7)             are still needed. In this variant the camera view is             presented together with the reticle as an all digital             picture on the display. This fully eliminates the need for a             mechanical adjustment of the reticle, see sketch in FIG. 2.             The calibration procedure is carried out as described above.     -   2. One embodiment comprises of a separate device attached to a         traditional optical sight. The separate device contains a camera         and processing unit and includes servo motors to be mounted onto         the existing adjustment screws. This variant can be used         together with traditional sights without any modification,         whenever a calibration is needed.     -   3. One embodiment is a semi-automatic device, according to         embodiment 1 and 2 above, where the device presents the shooter         with information about the needed adjustment, both in horizontal         and vertical directions, to achieve alignment between the bullet         hole and the reticle. The shooter then carries out the         adjustment manually according to the information

The current invention is based on a novel technique as compared to other closely related patents.

Bell describes an optical device for calibration of a sight, but the invention is based on other techniques than the current invention. Bell describes a method for establishing the difference between point of aim and point of impact, by the aid of a laser beam and mechanical arrangements for adjusting mechanical cross-hairs. Bell also relies on ballistical data. However, there is not mentioned any use of a camera and image analysis. Golubic discloses the comparison of a target image before firing with a target image after firing, but also relies on the projectile trajectory calculation for determining the error between point of aim and point of impact. Also parameters like temperature, wind direction elevation are used to calculate the trajectory and determine the error. The current invention is entirely based on image analysis of two images: one image taken just before firing that establishes the point of aim, and one image taken after firing that establishes the point of impact. There is no need for information on ballistical data or distance to target.

Towery et al describe the capability to record images taken at the firing moment by using separate sensors detecting either the recoil, sound or vibration from the firing mechanism, e.g. the firing pin striking the cartridge. A sight is described that include the capability to establish alignment between the reticle of the sight and the firearm bore by inserting/attaching a separate mechanical devices to the firearm bore e.g. which produces/reflects some kind of radiation, detectable by either the user or by automatic image analysis of images captured of said radiation. So, Towery describes an alignment between the sight and the rifle bore, which only provides a coarse adjustment of the sight. The invention presented in this document use a different technique compared to Towery and offers the ultimate exactness in terms of sight alignment, since it relies on image analysis only—no mechanical devices needed for determination of the error—even the detection of the firing moment is done through image analysis only.

Gordon describes a method for recording photographs in connection with the firing of a firearm, using a digital camera integrated with a rifle scope and detecting the firing moment using various techniques. The purpose of the device is strictly for the purpose of recording photographs and the device has no relation to calibration of a sight.

CITED REFERENCES

-   A U.S. Pat. No. 5,026,158 A, Golubic, Victor G. -   B U.S. Pat. No. 7,194,204 B2 Gordon, Jerry J. -   C U.S. Pat. No. 7,292,262 B2 Towery et al. -   D U.S. Pat. No. 7,363,742 B2 Nerheim, Magne H. -   E U.S. Pat. No. 7,624,528 B1 Bell et al. 

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 14. A device for the automatic calibration of a reticle in an optical sight for firearms, when shooting at a well defined target, assembled together with the sight, or as an attached separate device, characterized in that it includes; a digital camera for registration of the viewfinder image, a beam-splitter placed in such a manner that the shooter and the camera views the same scene, a processing unit for calculation of error and needed reticle correction, a memory for storing images, and a device for adjustment of the reticle.
 15. A device according to claim 14, characterized by the processing unit managing image capture and storing; one image just before the firing moment determining the point of aim, and one image after firing determining the point of impact.
 16. A device according to claim 14, characterized by the processing unit being designed for image processing operations for finding the target position, the reticle position which represents the point of aim in said image before firing, and also the target position, and projectile point of impact in said image after firing.
 17. A device according to claim 14, characterized by the processing unit being designed for calculation of the error between the point of aim and projectile point of impact.
 18. A device according to claim 14, characterized by the processing unit being designed for image analysis for detecting the rapid movement of the field of view, due to the recoil, thus capturing the last image before the firing moment.
 19. A device according to claim 14, characterized by the processing unit being designed to monitor the reticle movement during adjustment using camera images. 